A drill frequently used as a drilling tool is disposed with a cutting edge at an axial tip and a chip discharge flute in the axial direction and is rotated around an axial center to perform cutting with the cutting edge at the tip while discharging chips through the chip discharge flute. A three-flute drill disposed with three chip discharge flutes and three cutting edges at a tip is proposed as one type of such a drill. A drill described in Patent Document 1 is an example thereof and is disposed with a convexly-curved cutting edge portion formed into a convexly-curved shape convexed in the drill rotation direction on an outer circumferential end side of a cutting edge as well as a concavely-curved cutting edge portion formed into a concavely-curved shape concaved in the direction opposite to the drill rotation direction on an inner circumferential side of the convexly-curved cutting edge portion, and the convexly-curved cutting edge portion and the concavely-curved cutting edge portion are smoothly connected. In such a drill, an obtuse intersection angle is made between the cutting edge and a margin portion on an outer circumference of a drill main body, increasing the strength to suppress occurrence of cracking and chipping, and since the chips cut by the cutting edge are not broken at inner/outer circumferences of the cutting edge and the chips are curled and rolled into the inner circumferential side by the convexly-curved cutting edge portion, the chips are smoothly discharged and the tool durability is enhanced.